Filtering all posts in Rust

I always enjoy these sorts of posts: A developer starts with a specific goal in mind and an idea of how it might be accomplished. They proceed to run into a problem and rather than glossing over it, they document their debugging → understanding → fixing process. In this post the goal is to implement a binary tree data structure in Rust.

I particularly liked the optimisation section at the end. In my experience, it’s not uncommon for the first implementation that compiles and runs as expected to be fairly verbose. From there, optimising for usability and readability can be done fairly quickly though.

I’ve dubbed it the “Snook Algorithm” because as far as I know, it doesn’t have an official name. It’s the points-based system Jonathan uses (or perhaps used at this point) for filtering spam on snook.ca.

Let’s say you’re writing your own deployment solution in Rust. The basic flow you have in mind might go something like this:

Pull the latest commits down onto the server

Build the app (if it’s written in a compiled language)

Start the app

Move traffic to the new version of the app

Remove the old version

The problem is that you’ve already got the old version of the app running so the new version will fail to start because the port it requires is already taken. What you need is a way to find a port that’s available, tell the app to start on that port, and then redirect traffic upstream to it.

Route specific middleware is a fairly common need in web apps. As soon as you introduce something like authentication into the mix, you’ll probably want a way to apply middleware to routes you only want users to be able to access if they’re logged in.

As things stand, route specific middleware in Iron is a repetitive and messy business, which is where iron_middlefiddle comes in. It provides a macro which turns the tricky into the trivial, allowing you to add middleware to any number of routes within a Router easily.

With the addition of those tests, the library has reached a point where I feel comfortable in the thought of others using it. If no issues arise in the next month or so, I’ll bump this release to 1.0.0.

As we can see above, the code for setting a MIME type is generic and doesn’t need anything except a Response to modify. It is therefore a prime AfterMiddleware candidate, which once implemented will remove the need for the code repetition in each and every one of our routes’ handlers. Here’s a very brief AfterMiddleware description from the docs:

AfterMiddleware receive both a Request and a Response and are responsible for doing any response post-processing.

Back in February 2016, Jimmy Cuadra wrote a post about “The highs and lows of Rust”. He too came to Rust from dynamic web-focused languages and he too “clicked” with it:

Rust has a reputation of having a much higher learning curve [than Go], which of course affects its popularity. I really haven’t been able to understand why, but somehow Rust just clicks with my mental model of programming […]

I’ve been wondering what helped make Rust click for me. The best answer I have come up with is that its basic function structure is relatively familiar to anyone who’s worked with Javascript. function becomes fn, and the parameter and return types are typed but other than that it’s more or less the same. I think that that familiarity with such a core and highly used part of the language helps a lot.

The low points he addresses are interesting to look back on a year and a bit down the line. Serde has matured a lot, having recently reached 1.0.0, passed the 2 million downloads mark, reached number 9 on the “most downloaded” list and become the favoured serialization crate of the core Rust team who have deprecated their own serialization crate.

His thoughts once again echo my own when it comes to Rust’s usefulness:

While the language is described as a “systems language” and is generally intended for lower level applications, my domain is in higher level applications, and I’ve found Rust to be just as suitable and strong for my purposes. It really is a fantastic general purpose language.

Compiling to a binary, and thus taking away the need to setup a whole environment to run Ruby, Python, etc. programs, adds a level of portability and flexibility that (amongst other reasons) has made Rust my go-to even for for day-to-day scripts.

Argon2 is the password hashing algorithm that won the Password Hashing Competition in 2015. It is comprised of 2 main versions: Argon2i, which is optimised to resist side-channel attacks; and the version we’re interested in, Argon2d, which is optimised to resist GPU cracking attacks.

The argon2rs crate is a pure rust implementation of Argon2, which supports both of the above versions.

ReadDir provides an iterator over the contents of a directory. It’s worth noting that it’s a non-recursive iterator, which is why we’re using fs::remove_dir_all here. That standard function will delete a directory along with all of it’s contents, which avoids us having to recursively walk and delete. As I’m here, I’ll recommend the walkdir crate for all of your recursive walking needs though.

Note: In production, the delete_dir_contents function is the sort of thing you’d probably want to break out into a utils module.

Work continued on flyingV, one of my side-projects, last week. An interesting challenge I came up against was to find all of the matches to a particular regex across multiple files. For each match, I needed to save a specific portion of it then replace a specific portion of it with a new string.

The following uses the regex crate and is written in Rust. Captures are a feature of the regex language, not the regex crate itself though so if you aren’t familiar with them, there should still be something in this post for you.

To business then. The pattern I was matching against was any terafor loop containing quotes. Here’s an example loop I’d want to match:

Over the course of my time on the internet I have been a part of many different communities, from the household names to the highly niche.

If one thing can be learnt from them it’s that building a community is hard; building a welcoming, helpful, ludicrously smart community is nigh-on impossible.

Building one such community is something Mozilla has managed to do with Rust however. My first month using the language and interacting with it’s community has set a new gold-standard in my eyes for what a healthy community looks like.